Greater dapivirine release from the dapivirine vaginal ring is correlated with lower risk of HIV-1 acquisition: a secondary analysis from a randomized, placebo-controlled trial

Introduction A vaginal ring containing 25 mg of the antiretroviral dapivirine has demonstrated efficacy in reducing women’s risk of sexually acquiring HIV‐1; however, imperfect ring use likely diluted efficacy estimates in clinical trials. The amount of dapivirine remaining in returned rings may reflect the extent of product use, permitting estimation of HIV protection in the context of consistent use. Methods We measured the amount of dapivirine in returned rings from a placebo‐controlled trial of the dapivirine vaginal ring conducted between August 2012 and June 2015 among 2629 African women. Phase I/II studies established that greater than 4 mg of dapivirine on average is released from the ring when used consistently over 28 days and ≤0.9 mg released suggested non‐use. We assessed the relative risk reduction associated with levels of ring use using residual dapivirine in returned rings as a time‐dependent covariate for HIV‐1 infection in multivariable Cox models, including multiple exploratory analyses designed to estimate upper limits of efficacy given uncertainty in timing of HIV‐1 acquisition. All models were adjusted for baseline covariates associated with HIV risk and adherence. Results Residual dapivirine levels indicating at least some use (>0.9 mg released over a month) were associated with a 48% relative reduction in HIV‐1 acquisition risk (95% confidence interval (CI): 21% to 66%; p = 0.002) compared to the placebo. Exploratory analyses accounting for potential misclassification in timing of HIV‐1 acquisition estimated 75% to 91% HIV‐1 risk reduction with> 4 mg released when compared to placebo. Results limited to the subgroup of women